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Thyroxine safe with low TSH levels

New research shows it may be safe for patients taking thyroxine replacement to have low but not suppressed thyroid stimulating hormone (TSH) levels.
The research, presented at the Society for Endocrinology BES meeting in Manchester last week, shows that it may be safe for patients to take slightly higher doses of thyroxine than are currently recommended.

When treating hypothyroidism, clinicians aim to ensure that levels of TSH also remain in the normal range. TSH stimulates the thyroid gland to release thyroxine. Its levels are controlled by thyroxine in a negative feedback loop, with greater levels of thyroxine leading to a decreased TSH production. There have been concerns that abnormal TSH levels can lead to a greater risk of conditions such as heart disease and osteoporosis.
Dr Graham Leese, Ninewells Hospital and Medical School, led a team examining patients on thyroxine replacement therapy. They studied how variations in patients’ TSH levels affected their long-term health. The study followed 16,426 patients taking thyroxine (86 per cent female, mean age 60 years) and examined how their risk of contracting a range of diseases varied with their TSH levels.
The study found that patients with very high (>4.0mU/l) or suppressed (≤0.03mU/l) TSH levels more frequently suffered from heart disease, abnormal heartbeat patterns and bone fractures compared to patients whose TSH levels are in the normal range (0.4-4.0 mU/l). Patients who had a slightly low TSH level (0.04-0.4mU/l) did not have an increased risk of contracting any of these conditions.
These results show for the first time that it may be safe for patients taking long-term thyroxine replacement therapy to have a low but not suppressed TSH level.
These patients do not show an increased risk of suffering from heart disease, bone fractures or abnormal heartbeat patterns. This means that patients may be able to take slightly higher doses of thyroxine than are currently recommended without having an adverse effect on their health.